Thin-layer Absorption Research Articles

2D materials for infrared sensing and hyperspectral imaging

2D materials for sensing applications offer several advantages—high absorption in thin layers, the lack of surface dangling bonds or major defects, ease of materials synthesis and device fabrication, and relaxed substrate lattice-matching requirements. We theoretically explore two 2D materials, hexagonal boron phosphide and hexagonal boron arsenide, for possible infrared sensing and hyperspectral applications. Using first principles, we calculate the total energy of formation, band structures, and absorption coefficient of monolayer and bilayer materials. We evaluate the bandgap and absorption coefficient of bilayers as a function of layer stacking, number of layers, and applied field across the layers. We find that with a choice of stacking order, number of layers, and applied field, the material can be chosen appropriately for sensing of short-, mid-, or long-wavelength infrared radiation. Furthermore, the absorption is increased in these materials with applied electric fields. With the ability to dynamically change the bandgap with an external electric field, this class of materials is ideally suited for continuous hyperspectral sensing in the infrared.

Optical loss analysis of Sb2S3 and Sb2Se3 thin film solar cells: A Quantitative Assessment

Optical loss either by light reflection, or light absorption in different layers of a solar cell, can significantly impact short-circuit current density. In this paper, an optical model has been developed to analyze the optical loss in thin film solar cells made of CdS/Sb2S3 or CdS/Sb2Se3 antimony chalcogenide. This model is based on optical loss from absorption in thin layers and reflection at the interfaces of glass/TCO/CdS/(Sb2S3 or Sb2Se3) only by considering the optical properties of layers (refractive index and extinction coefficient). The transmission and reflection rate of Sb2S3 or Sb2Se3 show almost a similar trend. The absorptivity and relative loss in short-circuit current density (Jsc) versus the thickness of Sb2S3 and Sb2Se3 layers was calculated for two different structures: glass/TCO/CdS/Sb2S3 and glass/TCO/CdS/Sb2Se3. The Sb2Se3 solar cell shows a slightly better conversion performance compared to Sb2S3 solar cell due to lower reflection loss. The light reflection was calculated at four interfaces. The transmission rate of light through TCO, ITO, and CdS layers was calculated to obtain an optimal thickness for these layers. TCO showed a higher transmission rate and thus is preferred in antimony solar cell structures. The variations of (Jsc) and loss for Jsc with different thicknesses of ITO (>20%) or TCO (<20%) contact layers, favoring TCO for its lower optical losses and higher Jsc (24 mA cm−2).

Directional absorption by phased arrays of plasmonic nanoantennae probed with time-reversed Fourier microscopy

We demonstrate that an ordered array of aluminum nanopyramids, behaving as a phased array of optical antennae, strongly modifies light absorption in thin layers of dye molecules. Photoluminescence measurements as a function of the illumination angle are performed using a time-reversed Fourier microscope. This technique enables a variable-angle plane-wave illumination of nanostructures in a microscope-based setup. Our measurements reveal an enhancement of the light conversion in certain directions of illumination, which indicate the efficient diffractive coupling between the free space radiation and the surface plasmons. Numerical simulations confirm that surface modes supported by the periodic array enhance the intensity of the pump field in the space between particles, where the dye molecules are located, yielding a directional plasmonic-mediated enhancement of the optical absorption. This combined experimental and numerical characterization of the angular dependence of light absorption in nanostructures can be beneficial for the design and optimization of devices in which the harvesting of light plays a major role.

Plasmonic blackbody: Strong absorption of light by metal nanoparticles embedded in a dielectric matrix

We have experimentally and theoretically demonstrated strong absorption of visible light in a thin nanostructured layer consisting of silver nanoparticles embedded in a dielectric matrix. Light absorption at the level of above 90% is recorded over a wide optical wavelength range (240--850 nm) and for a broad range of angles of light incidence $(0\ifmmode^\circ\else\textdegree\fi{}--70\ifmmode^\circ\else\textdegree\fi{})$ in extremely thin films (160 nm). We suggest a generic principle for enhancement of light absorption in thin layers of artificial metamaterials and show that effective refractive indices of our samples measured with the help of ellipsometry can be adequately described by an effective-medium theory. We demonstrate that a substantial fraction of light can be trapped in the nanostructured film due to scattering by noble metal nanoparticles and total internal reflection.

Build up of 147Pm and 170Tm beta-ray bremsstrahlung in radiators of Al, Cu, Sn and Pb

The build up of bremsstrahlung intensity in metallic targets of Al, Cu, Sn and Pb by β-particles of 147Pm and 170Tm, non-unique first forbidden β-emitters, has been studied. The build up of bremsstrahlung has been described in terms of β-ray interaction and bremsstrahlung absorption in thin layers of targets. Magnetic field deflection and β-stopper techniques have been used to evaluate the integral bremsstrahlung intensities above 30 keV excited by 147Pm and 170Tm β-particles in targets of various thicknesses. The overall agreement between the measured and calculated curves is good over the entire range of β-particles. The results obtained on the build up of bremsstrahlung can help in determining the effectiveness of radiation shielding arrangements in space vehicles and electron accelerators.

Relation to Diffusion Measurements of Some Beta-Ray Absorption Phenomena

The absorption in thin layers of nickel, aluminum, and cobalt of beta rays from Co60 was measured in connection with the use of the surface counting method of determining diffusion coefficients. Data was obtained for foils and for evaporated and electroplated layers. In all cases the activity increased between 0 and 4 mg/cm2. A discrepancy was noted between the data for foils and those for evaporated and electroplated layers. It is shown that this general behavior is predicted by simple scattering and absorption expressions. The implications of these data for the use of the surface counting method are discussed.

Příspěvek k měření absorpce v tenkých vrstvách

Příspěvek k měření absorpce v tenkých vrstvách